1. Field of the Invention
Removal of proteins from aqueous media by precipitation.
2. Discussion of the Prior Art
Proteins have traditionally been removed from aqueous media through use of reagents or heat. Certain solvents (chloroform, urea) denature protein and cause its precipitation. Similarly, raising the electrolyte level of a medium to a high degree by addition of salts also precipitate the protein. Further, heat not only denatures but generally coagulates protein, thus separating it from aqueous media.
There are three major drawbacks to these methods of protein removal. First, the material removed from the medium is not purely protein. Instead, when the medium contains a complex mixture of chemicals as when the medium is a cell lysate, use of these methods may cause removal of other materials in addition to protein. Second, the protein removed by these methods is generally Irreversibly denatured or denaturable only by time consuming procedures such as dialysis. Third, either isolation or purification of the protein traditionally involved use of somewhat toxic solvents (phenol and/or chloroform).
A polymeric material described in U.S. Pat. No. 4,421,653 attempted to overcome these problems. That material, a polyethylene maleic anhydride derivative, cross-linked with diamine, however requires up to 9 volumes in solution, in order to deproteinate a single volume of blood serum. This great excess of the "deproteinizing agent" reveals its low efficiency and renders it unsuitably expensive for commercial processes. Furthermore, this matrix will precipitate proteins in the alkaline range (i.e., pH 10), thus rendering desorption of the desired protein from the matrix very difficult under mild alkaline conditions.
A novel approach to this problem is to be found in applicants earlier U.S. Pat. No. 5,294,681 and its continuation in part application now U.S. Pat. No. 5,453,493. Under certain circumstances however, problems of viscosity arise in the use of these novel compositions. It was therefore considered desirable to seek modifications of the compositions previously disclosed by applicant which avoid these viscosity problems.